Safety and health in mines research advisory board

Annual Review 2001

CONTENTS

FIRE AND EXPLOSION

Ventilation controlled fires in tunnels

This Health and Safety Laboratory (HSL) project is jointly funded by the
European Coal and Steel Community (ECSC) and the Health and Safety Executive
(HSE) mines and railways inspectorates. HSL’s part is an experimental
investigation of the conditions for and characteristics of ventilation controlled
tunnel fires - fires in which the heat output is related to the rate of supply
of air to the fire rather than the availability of fuel. This has particular
importance for:

The way in which such fires may be combated and especially the use of
ventilation to control smoke flow

The mix of combustion products from the fire

The rate of fire development

Progress has been made during 2001 towards finalising the experimental design
and programme to be carried out during the spring and summer of 2002. These
experiments will be conducted using 600 mm ducting and comprise two seats
of fire. The first will comprise a gas burner located near the duct inlet
merely to provide a vitiated atmosphere further downstream in the duct.
This atmosphere, characterised particularly in terms of oxygen, CO and CO2
concentrations, will then be used to ventilate a series of test fires using
a variety of materials including conveyer belting PMMA (Perspex - a common
fire test material), a flammable liquid pool and a wooden crib. Downstream
the duct will be instrumented with thermocouples, smoke opacimeters, load
cells and gas concentration sensors. Some initial experiments to examine
the variation of flame morphology with ventilation rate will be followed by
tests to measure the response of smoke generation, CO/CO2 ratio,
heat release rate and rate of flame spread with ventilation rate and the extent
of upstream vitiation.

Prediction of Fire Effects in mines

The University of Nottingham (UoN) are also now involved as partners in
the ECSC underground fires project, having taken over the contract from IMC
Technical Services (IMC-TS). UoN are to conduct a series of Computational
Fluid Dynamics (CFD) simulations to replicate a series of fire gallery tests
performed in 2000 by IMC at the former Swadlincote test facility and reported
in last year’s review. In spite of the delays caused by the contract
reallocation, the UoN team is on schedule to complete the work before the
end of 2002.

Fire Safety Testing of Conveyor Belts

The large scale test gallery facility at Swadlincote has been used for many
years for the assessment of the fire propagation properties of conveyor belting
intended for use underground in the UK and is referred to in BS 3289:1990.
Its imminent closure prompted HSE to sponsor Cerberus (Mining Acceptance Services)
Ltd to carry out a project with the following objectives:

To provide a full characterisation of the test gallery then used in the
UK for belt approvals by the belt manufacturers and industry.

To identify, characterise and develop small scale laboratory tests which
could be used to examine the fire behaviour of conveyor belts in the absence
of the large scale facility.

To seek and obtain some understanding of the importance of changes in
test conditions on the performance of belts currently used in UK mines by
testing over a wider range of conditions.

The main contributors to the project were Fenner Ltd, who are the only manufactures
of this type of conveyor belting in the UK, and Cerberus (Mining Acceptance
Services) Ltd, who continued to test conveyor belting following the privatisation
of British Coal.

The project satisfactorily achieved all three objectives. A new test method
has been provided together with drawings of the apparatus needed and proposed
acceptance levels.

The results have been published as Contract Research report 407/2002, which
is accessible on the HSE Website and in hard copy from HSE Books.
Subject to further discussion with the DMCIAC, the outcomes of the research
might form the basis of amendments to BS 3289, which is a standard referred
to in the Model Rules that accompany The Coal Mines (Owner’s Operating
Rules) Regulations 1993.

DEVELOPMENT OF AN UNDERGROUND FIRE SAFETY RISK ASSESSMENT

The aim of this HSL project is to produce a risk assessment tool to improve
fire safety systems and awareness in underground mines. This is to be achieved
by reviewing incident history for fires in both coal and non-coal mines, the
regulatory framework, and the inventory of combustible materials used underground,
along with the range of standard fire tests applied. This information is to
be input into a risk assessment framework, identified during the project,
to provide a means of quantifying the risks present by particular groups of
materials and benefits of applying conditions to their use and various possible
means of mitigation.

The assessment system has now been developed and passed to HSE’s Mines
Inspectorate, the project sponsors, for comment. Broadly it is based
on the use of a flow chart and a number of check sheets used to assign a simple
ranking to areas of possible concern. Those showing a high ranking,
either due to past involvement in incidents, the presence of fuels and ignition
sources together, or known susceptibility to standards of housekeeping or
maintenance are treated in further detail. The output of the system is a documented
record of all aspects of the areas considered, well considered fire suppression/detection
systems, and input into the mines fire and evacuation strategy through a knowledge
of the nature of possible fires and the number of personnel at risk.

Two applications of the methodology will be undertaken, viz: the assessment
of fires on conveyor systems and vehicles used underground. The system
might also be piloted in an audit of a mine’s fire safety strategy.

IGNITION HAZARD FROM CONVEYOR IDLER ROLLERS

Idler bearings used in coal mine belt-conveyers have long been recognised
as a potential fire source. They are designed to meet a L10 failure
rating: under full axial and radial load conditions, 10% of a sample of these
bearings are expected to fail within 106 revolutions. There
are many of these bearings in use underground and inevitably failures occur
which go undetected for long periods and in the past have led to lubricant
and coal dust accumulation fires. What is not so well understood is
whether bearing failures might present an ignition hazard in relation to flammable
gas and coaldust-air atmospheres by some mechanism other than that which results
in fire. The European Explosive Atmosphere Directive (ATEX) covers such
non-electrical ignition sources and European Standard PrEN13463-1 will require
the hazard to be assessed. This project was set up to get a better understanding
of what the hazard involves and the extent of the assessment which might be
appropriate.

HSL is working in conjunction with Continental Conveyers Ltd (CC), one of
the main suppliers of conveyer systems. The project is progressing on
two separate phases in parallel. These are:

To produce a literature survey, pulling together information on bearing
failure and frictional ignition.

To develop an apparatus that will deliberately fail roller bearings (25
mm inner diameter) by running them at their operational limits (1200 N radial
load and 570 rpm) for extended periods. At various stages in the failure
process temperature measurements of failing bearings will be made using
infrared thermography. In addition, flammable gas-air and dust-air atmospheres
will be exposed to the failing bearing to test for ignition.

The basic design of the apparatus, developed in conjunction with CC, was
completed by the year end and will use driving wheels to turn the roller avoiding
drive-belts, which CC found to have limitations in similar testing applications.

CFD modelling of gas flows in coal mine goafs

This three-year HSL project began in April 1999 and is part-funded by the
ECSC programme. The main objectives are to use computational fluid dynamics
(CFD) modelling to improve understanding and control of methane emissions
from the goaf and longwall faces. In addition CFD will be used to improve
understanding and control of spontaneous heating in the goaf by optimisation
of inert gas injection systems.

The control of methane emissions from goafs and at longwall faces has been
studied using two differing CFD approaches:

The first examined the flow in a longwall face, back return and goaf.
Three dimensional simulations have been undertaken to examine flow behaviour
and the build up of methane concentration at the return end of the face.
The effect of sealing efficiency on methane concentration at the face return
has been demonstrated.

The second set of simulations demonstrates an approach to the simulation
of methane drainage. CFD and geotechnical modelling have been used together
in these simulations. The geotechnical modelling allows rock permeabilities
to be calculated that are based on strata specific data and include influences
of mining on permeability, for example, fracture formation. More recently,
further simulations have been undertaken, improving the representation of
the strata and the methane drainage process in the CFD model.

Mines Rescue Arrangements – Future Options

IMC-TS completed a study for the HSE which examined (a) the present structure
for mines rescue within the UK, (b) the structures of other, overseas, mines
rescue organisations and (c) the structures of other search and rescue organisations.

During the study, discussions were held with all the principal mining organisations
within the UK who are associated with the UK Mines Rescue Scheme. These
included the MRSL functions at Mansfield, Dinas, Houghton-le-Spring and Crossgates,
UK Coal, Scottish Coal, Tower, Betws Anthracite and the Coal Authority.
Overseas mines rescue organisations examined included those in France at HBL,
Germany, Spain, the USA, Canada, Ukraine, Australia and the RSA. Outside
mining, discussions also took place with the DTLR search and rescue functions
within the Maritime and Coastguard Agency and the UK Fire and Rescue Service.

The study demonstrated that, throughout the world, there exists a wide range
of models for providing emergency services to mines. However, despite
each one purporting to provide adequate arrangements for an effective response
in the event of an incident, none provided the level of cover demanded in
the UK. Relatively few organisations guaranteed a response within one
hour and many only guaranteed attendance of a first response team, not the
first and second response teams.

The study concluded that the existing UK mines rescue arrangements provide
one of the most flexible and low cost means of ensuring effective mines rescue
cover to both large and small coal mine operators. The findings of the
investigation were presented to the DMCIAC at their meeting in January.
The final report should be published in 2002.